1. Field of the Invention
The present invention relates to an electric-acoustic transducer having dual voice coil drivers, and more particularly to an improved electric-acoustic transducer, which can achieve a reproduction of a broad frequency band with high power and high efficiency, even with an ultra slim or small dimension, proper for small electronic appliances such as a notebook computer, by employing dual voice coil drivers and auxiliary magnetic circuits.
2. Description of the Related Art
In general, a sound reproducer is classified into a horn speaker, a system speaker used in an audio-system of high-fidelity such as a component system and including a woofer, a midrange and a tweeter respectively covering a predetermined frequency band, a general speaker covering the entire frequency band by a single unit, a micro-speaker having an ultra-light and ultra-slim construction to be used in a micro-camcorder, a walkman, etc., a receiver used in a mobile communication terminal, an ear-phone having a construction partly inserted in a user""s ear, and a buzzer receiving only a specific frequency band.
In a conventional general speaker, a bobbin around which a voice coil is wound is placed in a magnetic gap of a magnetic circuit which comprises a single magnet disposed in a yoke and a top plate mounted on the magnet. Further, the top of the bobbin is fixed to a vibrating diaphragm with a damper, whose center is perforated in a circular shape and whose periphery is fixed to upper and lower portions of the frame. A center cap or a dust cap is assembled at the center of the vibrating diaphragm to cover the center hole of the bobbin.
In the meantime, a micro-speaker employed in a cellular phone, a camcorder, a notebook computer, a micro-cassette, etc., has an electrodynamic construction in which the height of the frame is lowered by omitting the damper, so as to achieve ultra slim and ultra small construction corresponding to the size decrease of the system employing the micro-speaker.
In such an electrodynamic speaker, as shown in FIG. 1a, a protector 1 covers over a frame having a configuration of a recess, and a terminal plate 9 is fixed to the rear surface of the bottom of the frame 2. A magnetic circuit is formed by a yoke 8 fixed to a middle portion of the bottom of the frame, and a fixed magnet 6 and a plate 7 fixed in the yoke 8. The edge of the vibrational diaphragm 3 is so fixed to the stepped portion of the frame 2 that a moving coil 5 fixed to the vibrational diaphragm 3 is movably placed in the air gap between the yoke 8 and the plate 7. In FIG. 1a, numerals 10 and 11 respectively designate a hole and a coil.
The electrodynamic type speaker as above is of a structure in which the attraction and repulsion caused due to a reaction of a non-alternating (a direct current) magnetic flux generated in a fixed magnetic circuit upon an alternating (an alternating current) rotation magnetic flux generated in a moving coil movable in an upward and downward direction vibrate both the vibrational diaphragm and the moving coil upwardly and downwardly to produce sound. That is, the electrodynamic type speaker is a speaker in which the permanent magnet is fixed and the moving coil is moved, so that sound is generated.
However, the electrodynamic type speaker shown in FIG. 1a has disadvantages that in the case where it is manufactured in a micro form in order to apply to a notebook computer, a mini-cassette tape player, and a mobile communication terminal, etc., it is impossible to reproduce an expansion of the ranges of a low-pitched sound and a high-pitched sound necessary for portable electronic appliances in terms of a structure of a speaker.
Furthermore, although a coil wire 11 for supplying electric energy to the moving coil 5 vibrating upwardly and downwardly is fixed by applying a firm adhesive on the opposite ends thereof and a soft adhesive on the middle portion thereof as shown in FIGS. 1a and 1b, a breaking of the coil may happen when an excessive input is applied.
Moreover, especially when the vertical height of the speaker is not more than four millimeters, it is disadvantageous in working efficiency due to the construction to connect the flexible wire and the coil 5 with the top of the bobbin on which the coil shorter than the above four millimeters is wound. In this case, the breaking of the coil happens when the vertical height fails to accommodate the width of the vibration of the coil at a high input.
In the case that the input is limited in consideration of the danger of the coil breaking, it is impossible to achieve a high output. Moreover, it is difficult to secure a sufficient space for the vertical vibration for the high output in the speaker.
For reference, in a micro-speaker currently on the market, a rated input of a product is 0.01 (W) to 0.1 (W) when its diameter is less than 20 mm, 0.2 (W) to 0.5 (W) when its diameter is 36 mm, and 0.5 (W) to 1 (W) when 50 to 57 mm.
In the meantime, an appliance such as a notebook computer having a display monitor employs a slim-type speaker mounted near the screen or in a housing of a personal computer. This type of speaker has an oval construction whose dimensions are in a range from 28 by 40 mm to 16 by 35 mm as its minimum. In the case of the speaker having the dimensions of 16 by 35 mm, it exhibits a reproduction band of 480 Hz to 16 KHz when the minimum height is 4.5 mm, and an output of 73 dB under 1 M/1 W.
As the decrease of the dimensions of the speaker which produces a variety of restrictions, the low band resonance frequency f0 is increased, and the efficiency and the output are decreased.
Meanwhile, in a practical use, the electrodynamic speaker based on the conventional electric-acoustic transducing principle is now utilized as a buzzer capable of reproducing only a single tone signal of a highly narrow one or two KHz.
Owing to the above reasons, there is a need in the art for a micro-speaker that can reproduce a sound of a broad band, receive a high input, and can be automatically embedded in a PCB of a set in all directions of 360 degrees without a soldering process in order to realize a multipurpose mini personal information processing terminal in the near future.
There is required a micro-speaker having the following characteristics and dimensions as a terminal for processing information: a reproduction frequency band of 200 Hz to 16 KHz; a longer axis of 13 mm, a shorter axis of 50 mm, and a height of 4.1 mm; a rated power of two watt; an output sound pressure level of 80 dB at a distance of one meter by an input of one watt; and a good assembling characteristic without using assembling screws.
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide an improved electric-acoustic transducer, which can achieve a reproduction characteristic of a broad frequency band with high power and high efficiency, even with ultra slim or small dimensions, proper for a small electronic appliance such as a notebook computer, by employing dual voice coil drivers and auxiliary magnetic circuits.
Another object of the invention is to provide an improved micro-speaker including a plurality of voice coil drivers which enable a high power and a high efficiency and prevent unbalanced vibrations which may happen due to the longer axis of the single driver of the prior art, thereby realizing a clear and clean reproduction of high quality sound.
It is still another object of the invention to provide an improved micro-speaker which has a function of a broad band frequency reproduction capable of performing functions of various portable electronic appliances such as a buzzer, a receiver, a micro-speaker, etc., by a single unit of mini-size.
It is still another object of the invention to provide an improved micro-speaker, in which not only the above-mentioned functions are implemented but automatic mounting/coupling of the speaker is enabled to make the automation of its manufacturing process easier.
In accordance with one aspect, the present invention provides an electric-acoustic transducer comprising:
a yoke having first to third recesses arranged in series at regular intervals;
first to third permanent magnets respectively received in the first to the third recesses, the first to the third permanent magnets being arranged in a same polar direction to generate non-alternating magnetic fields;
first and second plates respectively mounted on the first and the third permanent magnets to form first and second magnetic gaps between an upper end of the yoke and outer peripheries of the first and the second plates;
first and second coils respectively disposed in the first and the second magnetic gaps, the first and the second coils generating alternating magnetic fields of a same phase and being displaced up and down according to a cooperation with the non-alternating magnetic fields generated by the first to the third permanent magnets when an electric driving signal is applied from exterior;
a rectangular frame having a periphery extending at a right angle to a remaining portion of the frame to form a recess, the yoke being placed at a center of the frame and surrounded by the periphery; and
a vibrational diaphragm having a periphery supported by an upper end of the frame, the first and the second coils being attached to the vibrational diaphragm so that the vibrational diaphragm generates sound corresponding to the electric driving signal when the first and the second coils are displaced up and down.
The yoke for forming the first and the second magnetic gaps, the first and the third permanent magnets, and the first and the second plates form first and second magnetic circuits respectively for driving the first and the second coils, and the non-alternating magnetic flux generated from the second permanent magnet is added to non-alternating magnetic fluxes of the adjacent first and the second magnetic circuits. Therefore, the transducing efficiency is increased.
The frame further may comprise:
first and second penetrating spaces formed at both sides out of the yoke and communicating with an interior of the recess of the frame;
first and second guide means for forming first and second redundant leads in zigzag shapes, the first and the second redundant leads being drawn out through the first and the second penetrating spaces from the first and the second coils;
electrode terminals, through which the driving signal is applied from an exterior, having first to fourth electrode pads printed on a lower surface of the frame at both sides of the first and the second penetrating spaces, the first and the second redundant leads having opposite ends connected to the first to the fourth electrode pads, the first and the second electrode pads at a first side of the frame being connected to the third and the fourth electrode pads at a second side of the frame to thereby connect the first and the second coils in parallel to each other; and
soft molding materials filled in the first and the second penetrating spaces with surrounding the first and the second redundant leads, thereby preventing the first and the second redundant leads from breaking.
In this case, the first and the second guide means are eliminated after the first and the second redundant leads are fixedly connected to the first to the fourth electrode pads.
The vibrational diaphragm may include a body having a shape of a rectangular plate and an edge for fixing the body to the frame.
In addition, the vibrational diaphragm may comprise:
first and second portions extending laterally in cone shapes from the first and the second necks to which the first and the second coils are attached;
third to fifth portions respectively forming a dome shape in first to third dust caps, the first and the second dust caps being disposed in the first and the second necks, the third dust cap being placed on a second recess between the first and the second necks;
a sixth portion forming a plane surface between the first and the second necks;
a seventh portion for preventing a divisional resonance of the vibrational diaphragm at a range of middle and high pitch tones, the seventh portion discontinuously protruding with a constant width and a constant height along a center portion of the first to the sixth portions excepting a central portion of the first to the third dust caps; and
an edge formed integrally with the first to seventh portions, a body including the first to the second portions being supported by the frame.
Preferably, the electric-acoustic transducer may further comprise a reinforcing body for reducing nonlinear distortion of the vibrational diaphragm, the reinforcing body having a shape equal to a shape formed by the first to the sixth portions and being attached to a lower surface of the vibrational diaphragm, the reinforcing body having openings corresponding to center portions of the first to the third dust caps.
It is preferred that a plurality of pores are formed at a bottom of the frame to provide passages of sound and heat.
The electric-acoustic transducer of the invention may further include first to fourth engaging grooves respectively formed at the four corners of the lower surface of the frame, each of which is assembled by snap engagement with each of first to fourth snap engagement protuberances formed at a casing accommodating the speaker.
According to another aspect of the invention, provided is an electric-acoustic transducer comprising:
first and second yokes being spaced apart and respectively having first and second recesses;
first and second permanent magnets respectively received in the first and the second recesses, the first and the second permanent magnets being arranged in a same polar direction to generate non-alternating magnetic fields;
first and second plates respectively mounted on the first and the second permanent magnets to form first and second magnetic gaps between an upper end of the yoke and outer peripheries of the first and the second plates;
first and second coils respectively disposed in the first and the second magnetic gaps, the first and the second coils generating alternating magnetic fields of a same phase and being displaced up and down according to a cooperation with the non-alternating magnetic fields generated by the first and the second permanent magnets when an electric driving signal is applied from an exterior;
a rectangular frame having a periphery extending at a right angle to a remaining portion of the frame to form a recess, the first and the second yokes being placed at spaced two middle positions of the frame and surrounded by the periphery; and
a vibrational diaphragm having a periphery supported by an upper end of the frame, the first and the second coils being attached to the vibrational diaphragm so that the vibrational diaphragm generates sound corresponding to the electric driving signal when the first and the second coils are displaced up and down.
The first and the second coils are connected to each other in series or in parallel, and the latter is preferable in consideration of matching impedance.
According to another aspect of the invention, provided also is an electric-acoustic transducer comprising:
a yoke having first to third recesses arranged in series at regular intervals;
first to third permanent magnets respectively received in the first to the third recesses, the first to the third permanent magnets being arranged in a same polar direction to generate non-alternating magnetic fields;
a plate mounted on the second permanent magnet to form a magnetic gap between an upper end of the yoke and outer periphery of the plate;
a coil disposed in the magnetic gaps, the coil generating an alternating magnetic field and being displaced up and down according to a cooperation with the non-alternating magnetic field generated by the second permanent magnet when an electric driving signal is applied from an exterior;
a rectangular frame having a periphery extending at a right angle to a remaining portion of the frame to form a recess, the yoke being placed at a center of the frame and surrounded by the periphery; and
a vibrational diaphragm having a periphery supported by an upper end of the frame, the coil being attached to the vibrational diaphragm so that the vibrational diaphragm generates sound corresponding to the electric driving signal when the coil is displaced up and down.
In this case, the yoke for forming the magnetic gap, the second permanent magnet, and the plate form a first magnetic circuit for driving the coil, and the non-alternating magnetic fluxes generated from the first and the third permanent magnets are added to a non-alternating magnetic flux of the first magnetic circuit.
As described above, the present invention provides a speaker especially suitable for ultra small or ultra slim type products.
In the present invention, the increase of weight of the vibrating system due to the dual coil construction lowers the low pitch resonance frequency, thereby achieving capability of reproducing a wide band of frequency incorporating all the functions of various portable electronic appliances such as a buzzer, a receiver, a micro-speaker, etc.
Further, in the present invention, since the coils can be connected to the electrode terminals without using flexible wires, the risk of the coil breaking is eliminated. Also, a high input can be received due to the dual drivers and the auxiliary magnetic circuits, so that a characteristic of a high output and a high efficiency is achieved. Moreover, an automatic assembling or Counting of the speaker is possible without soldering by a snap engagement.
Therefore, the present invention precipitates realization of a portable data-processing terminal having multi-functions including visual, auditory, office working functions, etc.